Advanced Materials & Processes

NOV-DEC 2013

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

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i T S S e "Cold Spray Coating Deposition Mechanism on the Thermoplastic and Thermosetting Polymer Substrates" Amirthan Ganesan, Motohiro Yamada, and Masahiro Fukumoto Practical use of cold spray in polymer substrate is still in the fledgling phase. The interaction of metallic particles with polymer substrates is poorly understood, so a thick coating has not successfully been developed on polymer substrates. In order to rationalize as fully as possible the entire behavior of the high velocity particle with the polymer substrate, we used thermoplastic and thermosetting polymer materials as substrates. Particle behavior FIB bisection of spherical copper particle with the substrate was ob- embedded in the PVC substrate. served under various gas pressures and temperatures, and with various particle feed rates. Results show particle behaviors are unique with respect to the substrate. Metal particles do not experience any plastic deformation due to the soft nature of polymer substrates. Particles attach to the thermoplastic substrate either through adhesive bonding and/or mechanical interlocking, whereas only pure localized fracture was observed on the thermosetting substrate and thus no particles attached firmly on the substrate. ADVANCED MATERIALS & PROCESSES • NOVEMBER-DECEMBER 2013 13 JTST HIGHLIGHTS were examined from a cross-section of TBC, and experienced different numbers of thermal cycles and crack number, and the total length of cracks were measured to aim at understanding the failure mechanism. The TBC consists of coldsprayed NiCoCrAlTaY bond coat on IN738 superalloy and double layered Typical morphology of YSZ surface plasma-sprayed adhered to the substrate after the top 8YSZ with a columYSZ spalled when the TBC experienced nar grain structured thermal cycles to failure. YSZ interlayer of about 20 μm thick and about 230 μm lamellar YSZ. With each isothermal cyclic test, TBC samples were kept at 1150°C for 26 minutes then cooled to a temperature less than 80°C in four minutes by air forced cooling. Results show that cracks propagated primarily within lamellar-structured YSZ over the columnar YSZ along the lamellar interface. The measurement from the cross-section revealed that crack number and total crack length apparently increased with the increase of the number of thermal cycles. Cracks with a length less than a typical size of 200 μm accounted for the majority of cracks despite the number of thermal cycles during the test. A crack initiation and propagation model for plasma-sprayed TBC is proposed with a uniform distribution of circular cracks. 73

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